Field of the Invention
The present invention relates to a device for capturing road curve properties and calculating the maximum safe advisory speed.
Description of the Related Art
Technological advances in determining Road Curve speed has evolved over many years. Initial methods included using a level and a ruler to measure the super-elevation (i.e., bank angle) of a road curve and using survey techniques to estimate the radius of the turn. Later advances included the introduction of the Ball Bank Inclinometer/Accelerometer, such as shown by U.S. Pat. No. 2,831,266 to Dorn. The Ball Bank Inclinometer/Accelerometer is a device that displays the bank angle by reading the position of a ball suspended in a fluid filled curved clear glass tube. By holding the Ball Bank Inclinometer/Accelerometer level in a vehicle and driving the vehicle around a curve, the lateral acceleration could be observed. Then by selecting a preset limit, the driver, through trial and error, could determine the maximum speed that would stay within the preset limit.
Later advances replaced the Ball Bank Inclinometer/Accelerometer with a digital Inclinometer/Accelerometer, such as shown by U.S. Pat. No. 4,942,668 to Franklin. The digital devices provided a digital readout and an audible alert when the preset limit was exceeded. While this improved the accuracy of the reading by eliminating the driver's interpretation of the position of the ball, the process still required trial and error test runs and was subject to errors due to variations in vehicle speed. Lastly, the current technology required the operator to record the road that is being measured and to complete a report of the results manually.
The following patents and publications are hereby incorporated by reference. U.S. Pat. No. 4,445,118 is a navigation GPS system that was initially patented by NASA. This patent covers the technology for processing satellite based signals for determining location on the surface of the Earth. U.S. Pat. No. 6,523,409 to Brudis shows a roadway curve advisory speed determination system. Brudis describes a device that records the maximum lateral acceleration experienced by a vehicle by adding electrical sensors to a Ball Bank inclinometer. And, the DOT Federal Highway administration published document FHWA-SA-11-22 in June 2011 on a GPS Method for determining Curve Speed, documents a method for calculating road curve radius.
However, those previous technologies have a number of limitations. Using the Tilt Indicator (or Ball Bank) alone requires the operator to drive at a constant speed, record the speed of test, and simultaneously read the Ball Bank indicator. The testing requires multiple runs using “trial and error” to determine the maximum speed for achieving the lateral acceleration limits. Using two operators is more costly, but can reduce some of the error. But there is a large inherent error in reading and recording. Also errors are introduced by inconsistent driving speeds. Lastly, there is a labor intensive analysis that needs to be performed, post testing.
The Digital Inclinometer/Accelerometer reduced much of the read errors created by the Ball Bank solution. However, inconsistent vehicle speed, manual calculations, and post-test analysis still introduce additional labor and errors. This method also requires multiple runs as it is based on trial and error.
The Advisory Speed Meter, as shown in U.S. Pat. No. 6,523,409, automatically captures and records the maximum lateral acceleration experienced by a vehicle, but errors are still introduced by inconsistent vehicle speeds and manually processing the data post-test. This method is based on trial and error of various test runs.